Laser-cleaving of an optical fiber array with controlled cleaving angle

ABSTRACT

The present disclosure relates to a process by which an optical fiber array or a single optical fiber is cleaved with a laser-cleaving apparatus. The coating material is stripped or removed from a section of an optical fiber array or single optical fiber; a coated or ribbonized section of the optical fiber array or the single optical fiber is secured in a holder; the holder is aligned inside the laser-cleaving apparatus; the laser cleaves the stripped ends of the fibers in the optical fiber array or the single optical fiber; the laser-cleaved ends of the optical fiber(s) are then mechanically separated to remove the free ends from the optical fibers in the optical fiber array or the single optical fiber, leaving a cleaved array of optical fibers or a single cleaved optical fiber. The cleaving process enables the optical fiber array or single optical fiber to be cleaved at flexible locations along an optical fiber ribbon, optical fiber, or optical fiber apparatus (e.g., cleaving can be performed close to a ferrule end face) with no swelling, minimal cleave angle variation across the cores of the optical fibers, a controlled surface roughness of the optical fiber end faces, and high process yield.

PRIORITY APPLICATION

This application claims the benefit of priority of U.S. application Ser.No. 17/321,886, filed on May 17, 2021 and of U.S. ProvisionalApplication No. 63/030,473, filed on May 27, 2020, the contents of whichare relied upon and incorporated herein by reference in theirentireties.

FIELD OF THE DISCLOSURE

This disclosure relates generally to processing an optical fiber arraywith a laser-cleaving apparatus and more particularly, to cleaving anoptical fiber array with a laser-cleaving apparatus followed bymechanical separation of the cleaved ends of the optical fibers in theoptical fiber array.

BACKGROUND OF THE DISCLOSURE

Optical fibers are commonly used for voice, video, and datatransmissions in many different settings. In these settings whereoptical fibers are used, there are typically many locations where fiberoptic cables carrying the optical fibers connect to equipment or otherfiber optic cables. For example, in Micro-Electro-Mechanical-System(MEMS) applications, optical fibers (as part of optical fiber ribbons)are connected to a planar MEMS.

The emergence of MEMs applications and expanded beam connectors requireangled cleaving of the end faces of the optical fibers, which may bebuffered, ribbonized and/or packaged in cables, with minimum insertionloss and desirable performance. Normally, it is common to produce an 8°final angle tip on each optical fiber for coupling applications, tominimize back reflections.

The main methods used to obtain angled tips include: mechanicalcleavers, polishing tools, and lasers. The use of mechanical cleavers iscommon, despite the issues of wear and chipping angles. However, largeglass roll-off variations in the flatness of the core region of theoptical fiber and variations in cleave length and angles are challengesfor this method.

Mechanical polishing is another common method used. Polishing involves aholder supported at an angle while the optical fiber is mechanicallypolished at the desired angle. However, polishing is time consuming andgenerally increases the cost of the final product. Also, while multiplefibers can be secured in a holder to increase the efficiency of thepolishing step, it can be difficult to consistently achieve the samepolishing angle on the end faces of all the fibers.

Lasers (e.g., CO₂ lasers) have only recently been introduced to obtainangle cleaving and been used in mass production. However, due to thelarge beam size (i.e., longer wavelength) and thermal effects that meltrather than cleave the optical fiber, there are difficulties to reducethe heat affected zone and to minimize swelling of the optical fiberduring cleaving.

The respective technical challenges of each of the aforementionedtechniques necessitates a new approach for cleaving an array of opticalfibers at a precise angle.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to a process by which an array of opticalfibers or a single optical fiber is cleaved with a laser-cleavingapparatus. The coating material is stripped or removed from a section ofan optical fiber array or single optical fiber; a coated or ribbonizedsection of the optical fiber array or the single optical fiber issecured in a holder; the holder is aligned inside the laser-cleavingapparatus; the laser cleaves the stripped ends of the fibers in theoptical fiber array or the single optical fiber; the laser-cleaved endsof the optical fiber(s) are then mechanically separated to remove thefree ends from the optical fibers in the optical fiber array or thesingle optical fiber, leaving a cleaved array of optical fibers or asingle cleaved optical fiber. The cleaving process enables the opticalfiber array or single optical fiber to be cleaved at flexible locationsalong an optical fiber ribbon, optical fiber, or optical fiber apparatus(e.g., cleaving can be performed close to a ferrule end face) with noswelling, minimal cleave angle variation across the cores of the opticalfibers, a controlled surface roughness of the optical fiber end faces,and high process yield.

In one embodiment, a laser-cleaved optical fiber apparatus is provided.The laser-cleaved optical fiber apparatus includes: at least one opticalfiber housed within a ferrule, wherein the ferrule has a ferrule endface, wherein the at least one optical fiber has a fiber end faceincluding an end face core, each fiber end face of the optical fibershaving a surface area, the surface area comprising a rough area thatdefines at least a portion of the surface area; wherein the rough areahas a surface roughness between 0.1 μm and 0.5 μm root mean squared(rms) as measured by a confocal microscope; and wherein the end face ofthe at least one optical fiber is spaced from the ferrule end face at adistance between 1 micron and 50 microns.

In another embodiment, for the fiber end face, a remainder of thesurface area that excludes the rough area of the fiber end face has asurface roughness of less than 10 nm rms. In another embodiment, therough area of the fiber end face comprises at least 5% of the surfacearea. In another embodiment, the rough area of the fiber end facecomprises over 80% of the surface area. In another embodiment, the fiberend face has a surface roughness of less than 10 nm rms in the end facecore. In another embodiment, the fiber end face has a surface roughnessof between 0.1 μm and 0.5 μm rms in the end face core. In anotherembodiment, for the at least one optical fiber, the fiber end face has adiameter that is substantially consistent with a diameter of the opticalfiber measured at a distance of about 1 mm from the fiber end face, andwherein the fiber end face diameter and the optical fiber diameter havea difference of less than 0.2 μm. In another embodiment, the end facecore is substantially concentric with a fiber core of the optical fibermeasured at a distance of about 1 mm from the fiber end face, andwherein the end face core and the fiber core have an offset at the fiberend face less than 0.1 μm. In another embodiment, the fiber end face issubstantially flat with a cleave angle between 0 degrees and 15 degreesrelative to a longitudinal axis of each optical fiber.

In one embodiment, a method of laser-cleaving an optical fiber array isprovided. The method of laser-cleaving an optical fiber array includes:operating a laser system to create a perforation along at least oneoptical fiber of an optical fiber apparatus, wherein the optical fiberapparatus comprises the at least one optical fiber and a ferrule housingthe optical fiber, the ferrule having a ferrule end face, wherein thelaser system includes an ultrafast laser emitting a laser beam that isapplied to form the perforation on the at least one optical fiber; andseparating the at least one optical fiber along the perforation to formcleaved optical fibers; wherein each cleaved optical fiber of theoptical fiber array comprises a fiber end face having a surface area,the surface area including a rough area comprising at least a portion ofthe surface area; wherein the rough area has a surface roughness between0.1 μm and 0.5 μm root mean squared (rms) as measured by a confocalmicroscope; and wherein the perforation is spaced from the ferrule endface by a distance between 1 micron and 50 microns.

In another embodiment, the laser beam has a wavelength ranging between700 nm and 1400 nm, a pulse width between 5 picoseconds and 15picoseconds, and a repetition rate between 25 kHz and 75 kHz. In anotherembodiment, the ultrafast laser has a power output ranging between 1 Wand 40 W. In another embodiment, the laser system includes spatial lightmodulator, an optical relay and a focusing lens; wherein the laser beamis passed through the spatial light modulator, the optical relay and thefocusing lens to form an Airy beam. In another embodiment, the distanceis between 1 micron and 10 microns. In another embodiment, separatingthe optical fibers comprises applying pressurized air onto the opticalfiber array such that the optical fiber array is cleaved, wherein thepressurized air is applied at a pressure ranging between 25 psi and 50psi over a time interval ranging between 0.1 seconds and 1.5 seconds. Inanother embodiment, the pressurized air is applied to the optical fiberarray at an angle relative to a longitudinal axis of each optical fiberof the optical fiber array, the angle ranging between 30 degrees and 60degrees. In another embodiment, the perforation along the optical fiberarray comprises a plurality of holes with a pitch ranging between 1.0 μmand 5.0 μm.

In one embodiment, a method of laser-cleaving an optical fiber array isprovided. The method of laser-cleaving an optical fiber array includes:operating a laser system to form a perforation along each optical fiberof the optical fiber array of an optical fiber apparatus, wherein theoptical fiber apparatus comprises the optical fiber array and a ferrulehousing the optical fiber array, the ferrule having a ferrule end face,wherein the laser system includes an ultrafast laser emitting a laserbeam and wherein the laser beam is applied to form the perforation ontothe optical fiber array; mounting the optical fiber array onto amotorized stage, wherein a first section of the motorized stage includesa first clamp applied onto a first side of the perforation of theoptical fiber array, and wherein a second section of the motorized stageincludes a second clamp applied onto a second side of the perforation ofthe optical array; and separating the optical fibers of the opticalfiber array along the perforation to form cleaved optical fibers havingfiber end faces; wherein separating the optical fibers of the opticalfiber array along the perforation comprises applying tensile stress ontothe optical fibers along the perforation by moving at least one of thefirst section or the second section of the motorized stage along alength of the optical fibers; and wherein the ferrule end face is spacedfrom the optical fiber end faces by a distance between 1 micron and 10microns.

In another embodiment, the fiber end faces of the optical fiber arrayeach have a surface area and a rough area; and wherein the rough areadefines a portion of the surface area and has a surface roughnessbetween 0.1 μm and 0.5 μm root mean squared (rms) as measured by aconfocal microscope. In another embodiment, a remainder of the surfacearea that excludes the rough area of the fiber end face has a surfaceroughness of less than 10 nm rms. In another embodiment, the rough areaof each fiber end face comprises at least 5% of the surface area. Inanother embodiment, the rough area of each fiber end face comprises over80% of the surface area. In another embodiment, each fiber end face issubstantially flat with a cleave angle between 0 degrees and 15 degreesrelative to a longitudinal axis of each optical fiber. In anotherembodiment, the laser beam has a wavelength ranging between 700 nm and1400 nm, a pulse width between 5 picoseconds and 15 picoseconds, and arepetition rate between 25 kHz and 75 kHz. In another embodiment, theultrafast laser has a power output ranging between 1 W and 40 W. Inanother embodiment, the laser system includes a spatial light modulator,an optical relay and a focusing lens to form an Airy beam; wherein thelaser beam is passed through the spatial light modulator, the opticalrelay and the focusing lens to form an Airy beam to form an Airy beam.In another embodiment, the stage includes an upper stage and a lowerstage upon which the upper stage rests; and wherein the upper stage isangled with respect to an upper surface of the lower stage at an anglebetween −15 degrees and 15 degrees. In another embodiment, theperforation along the optical fiber array comprises a plurality of holeswith a pitch ranging between 1.0 μm and 5.0 μm.

Additional features and advantages will be set out in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the technical field of optical connectivity. It is to beunderstood that the foregoing general description, the followingdetailed description, and the accompanying drawings are merely exemplaryand intended to provide an overview or framework to understand thenature and character of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments. Features and attributes associated with anyof the embodiments shown or described may be applied to otherembodiments shown, described, or appreciated based on this disclosure.

FIG. 1 is a schematic of an example laser-cleaving apparatus accordingto the present disclosure;

FIG. 2 is a perspective view of a stage of the laser-cleaving apparatusof FIG. 1 ;

FIG. 2A is a schematic of the stage of FIG. 2 illustrating a method ofsecuring the coated or ribbonized portions an array of optical fibersfor achieving an angled cleave according to the present disclosure;

FIG. 3 relates to Example 1 and is an image of an optical fiber afterundergoing laser treatment by the laser apparatus of FIG. 1 ;

FIG. 4 is a perspective view of a mechanical separation apparatusaccording to the present disclosure;

FIG. 4A is an enlarged perspective view of a portion of the mechanicalseparation apparatus of FIG. 4 ;

FIG. 4B is a side view schematic of the mechanical separation apparatusof FIG. 4A omitting the optical fibers;

FIG. 5 is a perspective view of another mechanical separation apparatusaccording to the present disclosure;

FIGS. 6A-6C relate to Example 1 and are microscope images of an end faceof an optical fiber after undergoing laser treatment by the laserapparatus of FIG. 1 ;

FIGS. 7A-7C relate to Example 1 and show results of a plane-wavedecomposition model simulation of Bessel beams impinging on an opticalfiber at a perpendicular angle relative to a longitudinal axis of theoptical fiber with a varying offset in the y-direction as shown anddefined in FIGS. 7A-7C;

FIGS. 8A and 8B relate to Example 1 and show top and side views,respectively, of microscopic images of the laser-cleaved ends of anarray of optical fibers;

FIGS. 9A and 9B relate to Example 1 and show images of cleaving qualityof an array of optical fibers prior to fusion splicing and after fusionsplicing, respectively;

FIGS. 10A and 10B relate to Example 2 and are microscope images of thelaser-cleaved end of an array of ribbonized optical fibers;

FIG. 11 relates to Example 2 and shows an end face of an optical fiberafter mechanical separation by a pressurized air jet in accordance withthe present disclosure;

FIG. 12 relates to Example 2 and an end face of an optical fiber aftermechanical separation by tension in accordance with the presentdisclosure;

FIG. 13A relates to Example 3 and shows a simulation of the intensityprofile (seen in XZ plane) of a Bessel beam directed to the center of atilted optical fiber end face when assuming the optical fiber is placedin air;

FIG. 13B relates to Example 3 and shows a microscopic image of theoptical fiber end face of FIG. 13A;

FIG. 13C relates to Example 3 and shows a simulation of the intensityprofile (seen in XZ plane) of a Bessel beam launched to the center ofthe tilted optical fiber end face while the optical fiber is immersed inwater;

FIG. 13D relates to Example 3 and shows a microscopic image of theoptical fiber end face of FIG. 13C;

FIG. 13E relates to Example 3 and shows a side view image of awater-assisted laser-cleaved optical fiber;

FIG. 13F relates to Example 3 and shows a simulation of refraction ofBessel beams incident on an optical fiber surface immersed in water;

FIG. 14A shows an example cubic phase mask in accordance with thepresent disclosure;

FIG. 14B shows propagation of an Airy beam after focusing by a focusinglens having a numerical aperture of 0.5 in accordance with the presentdisclosure;

FIG. 15 relates to Example 4 and is a schematic of a laser apparatus toproduce an Airy beam in accordance with the present disclosure;

FIGS. 16A-16C show example Airy beam amplitude shapes in variousconfigurations in accordance with the present disclosure;

FIGS. 16D-16F relate to FIGS. 16A-16C and show resulting focal spotshapes of FIGS. 16A-16C in accordance with the present disclosure;

FIGS. 17A-17C relate to Example 4 and show images of a fiber cleavedwith an Airy beam with the Airy beam's curve being perpendicular to acutting direction in accordance with the present disclosure;

FIGS. 17D-17F relate to Example 4 and show images of a fiber cleavedwith an Airy beam with the Airy beam's curve being parallel to a cuttingdirection in accordance with the present disclosure; and

FIGS. 18A-18B relate to Example 4 and show laser damage lines inrelation to a ferrule end face.

DETAILED DESCRIPTION

Various embodiments will be clarified by examples in the descriptionbelow. In general, the present disclosure relates to a process by whichan array of optical fibers or a single optical fiber is cleaved with alaser-cleaving apparatus. The coating material is stripped or removedfrom a section of an optical fiber array or single optical fiber; acoated or ribbonized section of the optical fiber array or the singleoptical fiber is secured in a holder; the holder is aligned inside thelaser-cleaving apparatus; the laser cleaves the stripped ends of thefibers in the optical fiber array or the single optical fiber; thelaser-cleaved ends of the optical fiber(s) are then mechanicallyseparated to remove the free ends from the optical fibers in the opticalfiber array or the single optical fiber, leaving a cleaved array ofoptical fibers or a single cleaved optical fiber. The cleaving processenables the optical fiber array or single optical fiber to be cleaved atflexible locations along an optical fiber ribbon, optical fiber, oroptical fiber apparatus (e.g., cleaving can be performed close to aferrule end face) with no swelling, minimal cleave angle variationacross the cores of the optical fibers, a controlled surface roughnessof the optical fiber end faces, and high process yield.

In this disclosure, the term “optical fiber” (or “fiber”) will be usedin a generic sense and may encompass single, individual optical fibers,bare optical fibers, coated optical fibers, buffered optical fibers,optical fiber ribbons, a planar array of coated optical fibers, or aribbonized array of coated optical fibers as well as optical fibersincluding different sections corresponding to these fiber types, unlessit is clear from the context which of the types is intended. “Bareoptical fibers” (including “bare glass optical fibers”) or “baresections” are those with no coating present on the fiber cladding.“Coated optical fibers” or “coated sections” include a single ormulti-layer coating (typically an acrylate material) surrounding thefiber cladding and have a nominal (i.e., stated) diameter that istypically no greater than twice the nominal diameter of the bare opticalfiber. “Buffered optical fibers” or “buffered sections” are coatedoptical fibers with an additional buffer that increases the nominaldiameter of the optical fiber to more than twice the nominal diameter ofthe bare optical fiber, with 900 μm being the most typical nominaldiameter. Buffered optical fibers may also be referred to as “bufferedcables.” Finally, the term “unbuffered optical fibers” refers to opticalfibers without a buffer, and therefore may encompass either bare opticalfibers, coated optical fibers or coated optical fibers which have apigmented outer coating layer.

In certain embodiments, pre-coated (i.e., acrylate coated) opticalfibers are prepared for cleaving and other downstream optical fiberprocessing (e.g., fusion bonding) by stripping the ends thereofutilizing non-contact fiber stripping methods and/or apparatuses, suchas those disclosed in U.S. Pat. No. 9,167,626 B2 (“the '626 Patent”),which is hereby incorporated by reference. Briefly, the '626 Patentdiscloses use of a heater configured for heating a heating region to atemperature above a thermal decomposition temperature of at least onecoating of an optical fiber, a securing mechanism for securelypositioning a lengthwise section of the optical fiber in the heatingregion, and a controller operatively associated with the heater andconfigured to deactivate the heater no later than immediately afterremoval of the at least one coating from the optical fiber. Thermaldecomposition of at least one coating of an optical fiber reduces orminimizes formation of flaws in optical fibers that may be generated bymechanical stripping methods and that can reduce their tensile strength.

In certain embodiments, unjacketed optical fiber segments emanating fromthe same jacket may be initially loose, but subsequently ribbonized toprovide consistent spacing between fibers to facilitate cleaving and/ordownstream optical fiber processing (e.g., utilization of a mass fusionsplicing process for forming multiple splice joints between multiplepairs of optical fibers in a substantially simultaneous manner). Tofabricate an optical fiber ribbon, optical fibers of an unjacketedsegment may be contacted with at least one polymeric material (e.g., athermoplastic hotmelt material) in a flowable state, and the at leastone polymeric material may be solidified.

Optical fibers of a first plurality of optical fiber segments and of asecond plurality of optical fiber segments may be arranged in first andsecond conventional fiber sorting fixtures, respectively, duringstripping and/or subsequent optical fiber processing steps (e.g., fusionbonding steps). A typical fiber sorting fixture includes a slot havingan opening dimension (e.g., height) that closely matches a correspondingdimension of unbuffered, coated optical fibers to maintain portions ofthe optical fibers proximate to ends to be stripped (and subsequentlycleaved and/or fusion spliced) in fixed, substantially parallelpositions embodying a one-dimensional array. In certain embodiments,coated optical fibers having outer diameters of either 200 μm or 250 μmmay laterally abut one another in a fiber sorting fixture, such thatcores of adjacent optical fibers are also spaced either 200 μm or 250 μmapart. After stripping of acrylate coating material from end sections(to form stripped sections) of the optical fibers, the remaining (bareglass) cladding and core portions are in a non-contacting (andnon-crossing) relationship, and bare glass ends of the optical fibersmay be cleaved as discussed below. Variations of the techniquesdisclosed in the '626 Patent are disclosed in U.S. Pat. Nos. 10,018,782and 9,604,261, the disclosures of which are also hereby incorporated byreference herein. Non-contact stripping methods using lasers or hotgases are also possible in certain embodiments.

Referring to FIG. 1 , a laser-cleaving apparatus 100 is shown.Laser-cleaving apparatus 100 is configured to cleave the stripped endsof an array of optical fibers 124 with coated or ribbonized regions thatare secured into stage 110 as discussed below. In particular, asdiscussed in greater detail herein, laser-cleaving apparatus 100 createsa series of apertures 126A (FIG. 3 ) in each of the optical fibers inthe optical fiber array 124 to form a perforation 126 (FIG. 3 ). In oneembodiment, the optical fibers in the optical fiber array 124 have coreand cladding diameters of about 9.0 and 125 μm, respectively. However,it is contemplated that alternate optical fibers with alternate core andcladding dimensions may be used in the context of the presentdisclosure. While reference is made to optical fiber arrays 124, it iswithin the scope of the present disclosure that laser cleaving apparatus100 and the techniques described in the present disclosure can beapplied to a single optical fiber 124A or multiple optical fibers 124A,such as optical fiber array 124.

Apparatus 100 includes a laser 102, a shutter 104, a reflecting mirror106, a series of lenses 108, and a stage 110. As shown in FIG. 1 , laser102 emits a laser beam 120 in the y-direction of the Cartesiancoordinate system as defined in the Figure. Laser beam 120 has awavelength in the range of 500 nanometers (nm) and 2000 nm, 600 nm and1700 nm, or 700 nm and 1400 nm. In one embodiment, laser beam 120 has awavelength of 1030 nm. In another embodiment, laser beam 120 has awavelength of 512 nm. In another embodiment, laser beam 120 has awavelength of 515 nm. In another embodiment, laser beam 120 has awavelength of 1064 nm. In some embodiments, laser beam 120 has a focalregion ranging between 1 micron and 10 microns in width. In someembodiments, laser beam 120 has a focal length greater than 100 microns.In some embodiments, laser 102 is an ultrafast laser. However, it iscontemplated that in alternate embodiments, a different suitable type oflaser may be used. In some embodiments, laser 102 emits laser beam 120at a pulse width between 1 picoseconds (ps) and 20 ps, 3 ps and 17 ps,or 5 ps and 15 ps. In one embodiment, the pulse width of laser beam 120emitted from laser 102 is 10 ps. In some embodiments, laser 102 emitslaser beam 120 at a repetition rate ranging between 15 kilohertz (kHz)and 100 kHz, 20 kHz and 85 kHz, or 25 kHz and 75 kHz. In one embodiment,laser 102 emits laser beam 120 at a repetition rate of 50 kHz. In someembodiments, laser 102 emits laser beam 120 at an output power rangingbetween 1 Watt (W) and 40 W, 1 W and 10 W, 3 W and 9 W, or 5 W and 8 Wwith a corresponding actual laser energy used for perforating an opticalfiber ranging between 80 μJ per pulse and 160 μJ per pulse. In oneembodiment, laser 102 emits laser beam 120 at an output power of 8 Wwith a corresponding actual laser energy used for perforating an opticalfiber of 112 μJ per pulse (about 70% of maximum pulse energy).

As mentioned previously, laser beam 120 passes through shutter 104.Shutter 104 is configured to control the exposure of laser beam 120 tothe remainder of laser-cleaving apparatus 100. When shutter 104 isopened, laser beam 120 passes through shutter 104 and moves toreflecting mirror 106.

Reflecting mirror 106 is configured to reflect laser beam 120 in adifferent direction than the direction when emitted by laser 102. Asshown, reflecting mirror 106 reflects laser beam 120 such that laserbeam 120 moves in a direction that is substantially perpendicular (ororthogonal) relative to the previous direction. Stated another way, asshown in FIG. 1 , laser beam 120 is moving in the y-direction and uponcontacting reflecting mirror 106, laser beam 120 moves in thez-direction. In alternate embodiments, other various angle reflectionsmay be possible relative to the incoming direction via reflecting mirror106.

Laser beam 120 then proceeds through a series of lenses or optics 108that are controlled by a translation stage 122. As shown in FIG. 1 ,lenses 108 include an axicon lens 108A, a convex lens 108B, and anobjective lens 108C. Lenses 108 are configured to create a Bessel beam109 and focus Bessel beam 109 onto an optical fiber array 124 seated onstage 110 as described below. In alternate embodiments, other series andcombinations of lenses and/or different lenses (e.g., a pair ofcollimating lenses) and/or other optics (e.g., spatial light modulator(SLM)) may be used to create and focus Bessel beam 109 onto opticalfiber array 124 and are contemplated in the present disclosure.

Translation stage 122 controls the positioning of the series of lenses108 between reflecting mirror 106 and stage 110 along the z-axis asshown in FIG. 1 . Translation stage 122 is operably connected tocomputer 116 and driver 118 such that computer 116 provides instructionsto driver 118, and driver 118 moves translation stage 122 according tosuch instructions. In this way, laser beam 120 undergoes beam shaping asdiscussed below and is focused onto optical fiber array 124. Beamshaping is a process of redistributing the irradiance or phase of anoptical radiation using a purpose designed optical element with asuitable lens or several lenses. In one embodiment, laser beam 120 isshaped from a Gaussian beam to a Bessel beam via beam shaping by lenses108 and translation stage 122. In some embodiments, lenses 108 may bemodified such that laser beam 120 is shaped from a Gaussian beam to anAiry beam as discussed herein. In one embodiment, laser beam 120 has aspot size of about 1 μm with a relative long line of focus of about 1 mm(which can fully cover the entire diameter of optical fiber array 124)after passing through lenses 108. In one embodiment, the velocity oftranslation stage 122 is about 20 mm/s.

After passing through lenses 108, laser beam 120 (also referred to as“Bessel beam 108”) is focused onto optical fiber ribbon 124 that ispositioned on stage 110. As mentioned previously, in one embodiment,optical fibers of optical fiber array 124 have core and claddingdiameters of about 9.0 and 125 μm, respectively. However, it iscontemplated that alternate optical fibers may be used in the context ofthe present disclosure. The coated ends of the fibers in the opticalfiber array is stripped (e.g., thermally or the like) after the opticalfiber jacket (not shown) is removed, and optical fiber ribbon is cleanedby methods known in the art. A coated region of the fibers in the arrayof optical fibers or of the optical fiber array 124 is then clamped ontoa fiber holder prior to mounting optical fiber array 124 onto stage 110.

Stage 110 includes an upper stage 114 and a lower stage 112. As shown inFIGS. 1 and 2-2A, upper stage 114 is configured to support optical fiberarray 124 upon top surface 117. Stated another way, a coated orribbonized region of the optical fiber array 124 and the fiber holderare mounted onto upper stage 114. Upper stage 114 comprises a tiltablestructure 115 that can angle optical fiber ribbon 124 at an angle αrelative to upper surface 119 of lower stage 112. In some embodiments,angle α (FIG. 2A) ranges between −15 degrees and 15 degrees relative toupper surface 119. By angling optical fiber array 124 via tiltablestructure 115, an angled cleave of optical fiber ribbon 124 can result.In some embodiments, the angle of the angle cleave ranges between 0degrees and 15 degrees relative to a longitudinal axis of each opticalfiber of optical fiber ribbon 124.

Lower stage 112 supports upper stage 114 along upper surface 119 (oflower stage 112) and is operably connected to driver 118 and computer116. Computer 116 and driver 118 operate to move lower stage 112 andstage 110 along the x-axis and the y-axis during operation of apparatus100 in order to cleave the optical fibers in optical fiber array 124. Inone embodiment, lower stage 112 has a resolution of about 0.01 μm. Inanother embodiment, lower stage 112 has a velocity of about 20 mm/sduring laser treatment or laser-cleaving (e.g., fabrication) of opticalfiber array 124.

To operate apparatus 100, a coated or ribbonized portion of the opticalfiber array 124 is placed and secured onto upper stage 114 of stage 110.Then, laser 102 is activated to emit laser beam 120. In one embodiment,laser 102 emits laser beam 120 at a wavelength of 1030 nm, a pulse widthof 10 ps, a repetition rate of 50 kHz, and an output power of 8 W. Laserbeam 120 is emitted from laser 102 and travels throughout apparatus 100as shown in FIG. 1 (i.e., passing through shutter 104, reflecting offreflecting mirror 106, and passing through lenses 108) such that laserbeam 120 passes across the optical fiber array 124 to createperforation(s) on the optical fibers in optical fiber array 124 asdiscussed below. Stated another way, apparatus 100 provides a singlepass laser 102 and laser beam 120 across the optical fibers in opticalfiber array 124 to sequentially create perforation(s) in each opticalfiber in optical fiber array 124.

Referring to FIG. 3 , an image of an optical fiber 124A in optical fiberarray 124 is shown after undergoing laser treatment administered byapparatus 100. As shown, optical fiber 124A includes a plurality ofapertures 126A to form a perforation 126. In one embodiment, apertures126A have a pitch ranging between 1.0 μm and 5.0 μm. In one embodiment,the pitch between apertures 126A is about 2.4 μm. Pitch as discussedherein refers to the distance between a center of one aperture 126A to acenter of another adjacent aperture 126A.

Once perforation 126 is formed on each of the optical fibers in theoptical fiber array 124, the optical fibers in optical fiber array 124are separated along perforation 126 to remove the free ends 125 of theoptical fibers in the optical fiber array 124 and to complete thecleaving process of the optical fiber array 124. Referring now to FIG. 4, a separation apparatus 200 is provided to separate the free ends ofthe optical fibers in the optical fiber array 124 along perforation 126.Apparatus 200 includes a stage 202 upon which optical fiber array 124and a pressurized air jet 208 are positioned. As shown in FIG. 4A, airjet 208 includes a nozzle 210 and applies pressurized air 212 onto theoptical fiber array 124 and perforation 126 such that the free ends 125of the optical fibers in the optical fiber array 124 are removed alongperforation 126. Pressurized air 212 is applied onto optical fiberribbon 124 with an exposure time ranging between 0.1 seconds and 5seconds, between 0.1 seconds and 3 seconds, or between 0.1 seconds to 1second and an amount of pressurized air ranging between 1 pounds persquare inch (psi) to 50 psi, between 5 psi and 50 psi, or between 10 psiand 50 psi.

In one embodiment, the exposure time and amount of applied pressurizedair 212 is 0.3 seconds and 40 psi, respectively. FIGS. 4A and 4B showpressurized air 212 being administered at an angle β relative to stage202. In some embodiments, the angle β ranges between 30° and 60°. It iswithin the scope of the present disclosure that pressurized air 212 canbe administered substantially parallel to stage 202. Additionally, thedistance between the nozzle of air jet 208 and optical fiber array 124can be varied.

Referring now to FIG. 5 , an alternative separation apparatus 300(hereinafter referred to as “tension apparatus 300”) is shown. Tensionapparatus 300 includes a stage 302 that has a first section 302A and asecond section 302B where at least one of first section 302A and secondsection 302B is motorized. First section 302A includes a clamp 304 thatclamps onto a coated region of optical fiber array 124 on one side ofperforation 126 and holds optical fiber array 124 in place on stage 302.Second section 302B includes a clamp 306 that holds optical fiber array124 opposite clamp 304 and on the other side of perforation 126 asshown.

To operate tension apparatus 300, optical fiber array 124 is placed ontostage 302 with perforation 126 positioned between first section 302A andsecond section 302B of stage 302. Optical fiber array 124 is clampedonto stage 302 by clamps 304, 306 as discussed above. Second section302B remains static while first section 302A moves along a direction Ain line with longitudinal axis A1 of optical fiber array 124 to applytensile stress onto optical fiber array 124 along perforation 126. In analternate embodiment, second section 302B moves along longitudinal axisA1 of optical fiber array 124 while first section 302A remains static toapply tensile stress onto optical fiber array 124 along perforation 126.In another alternate embodiment, first section 302A and second section302B both move to apply tensile stress onto optical fiber array 124along perforation 126. It is within the scope of the present disclosurethat the translation velocity and ramp rate of first section 302A andsecond section 302B can be precisely controlled.

Referring now to FIGS. 6A-6C, images of an end face 127 (also referredto as “optical fiber end face 127” or “fiber end face 127”) of anoptical fiber of optical fiber array 124 (after laser-cleaving andmechanical separation) are shown. As shown in FIG. 6A, optical fiberarray 124 has been laser-cleaved by apparatus 100 in laser direction LDas indicated. In addition, optical fiber array 124 has been mechanicallyseparated by apparatus 200 along the perforation (not shown) in movingdirection MD as shown. Upon cleaving and separation, optical fiber endface 127 as shown in FIGS. 6A and 6B has a surface profile that variesabout optical fiber end face 127. In particular, optical fiber end face127 has a substantially symmetrical surface profile pattern where thesurface variation about optical fiber end face 127 varies by less than 1micron (μm). Such a low surface variation about optical fiber end face127 can be resolved (i.e., reflowed or compensated) when splicing withanother optical fiber.

Optical fiber end face 127 has a surface area SA that includes a rougharea RA comprising a portion of the surface area of optical fiber endface 127, and the rough area RA has a corresponding surface roughness.In some embodiments, optical fiber end face 127 has a rough area RAcomprising at least 5% of the surface area. In another embodiment,optical fiber end face 127 has a rough area RA comprising over 80% ofthe surface area of optical fiber end face 127. In another embodiment,the rough area RA of optical fiber end face 127 has a surface roughnessof between 0.1 μm and 0.5 μm root mean squared (rms) as measured by alaser confocal microscope (e.g., LSM 700, Zeiss). In other embodiments,the remainder of the surface area of optical fiber end face 127(excluding the rough area) has a surface roughness of less than 10 nmrms. In particular, in terms of surface roughness, fiber core 129 (alsoreferred to as “core 129”) has a surface roughness of between 0.1 μm rmsand 0.5 μm rms in some embodiments. In another embodiment, fiber core129 has a surface roughness of less than 10 nm rms. Referring briefly toFIG. 6C, a surface roughness plot is shown corresponding to opticalfiber end face 127 shown in FIGS. 6A-B. In FIG. 6C, the surfaceroughness is about 0.5 μm, which is suitable for future splicing withother optical fibers.

Referring in particular to FIG. 6B, the rough area of optical fiber endface 127 does not include fiber core 129. Stated another way, aspreviously discussed, fiber core 129 is substantially unaffected by theroughness of optical fiber end face 127 that is imparted uponlaser-cleaving and mechanical separation. In this way, the optical fiberperformance (i.e., insertion loss) is substantially unaffected by thelaser-cleaving and mechanical separation processes described above.Without wishing to be held to a particular theory, it is believed thatthe geometry of optical fibers of optical fiber array 124 (e.g., curvedshape) can act as a lens to shape incident laser beam 120. That is, thegeometry of optical fibers of optical fiber array 124 either distortand/or refract laser pulses of laser beam 120 when laser beam 120 andthe surfaces of the optical fibers in optical fiber array 124 are at anoblique angle with respect to one another or move laser pulses of laserbeam 120 forward when laser beam 120 and the surface of the opticalfibers in optical fiber array are perpendicular to each other. Withoutwishing to be held to a particular theory, it is believed that the laserpulse of laser beam 120 does not affect the fiber core region due to thelensing effect (distortion and/or refraction) of the surfaces of theoptical fibers in optical fiber array 124 and limited pulse energy.

Also, the laser-cleaving and mechanical separation processes describedabove substantially maintain the concentricity of fiber core 129 alongoptical fiber 124A. That is, the laser perforation 126 formed byapparatus 100 and the subsequent separation process by either apparatus200, 300 do not substantially deform optical fiber 124A and fiber core129. In some embodiments, fiber core 129 at fiber end face 127(hereinafter referred to as “end face core”) is substantially concentricwith a fiber core of optical fiber 124A measured at a distance (e.g.,about 1 mm) from fiber end face 127, wherein the end face core and thefiber core have an offset of less than 0.1 μm.

In alternate embodiments, alternative methods for cleaving an opticalfiber array with subsequent separation are contemplated in thisdisclosure such as water-based cleaving as discussed below and in theExamples.

In an alternate embodiment, as mentioned above, an airy beam 130 may beused to treat optical fibers 124A or optical fiber array 124. Except asnoted herein, details regarding the cleaving process, the cleave itself,and the optical fiber 124, 124A surface properties of the Bessel beamembodiments described above are substantially consistent with thisembodiment described below. Airy beams 130 have similar properties interms of wavelength and focal range as described above. To generate Airybeam 130, laser apparatus 200 may be used as discussed below withreference to FIG. 15 . In particular, a Gaussian beam (e.g., laser beam120 with the properties discussed above) emitted in laser apparatus 200can be modified by applying a cubic phase function and a FourierTransform using a focusing lens 204 (FIG. 15 ). In some embodiments, acubic phase function ϕ is shown in Equation 1 below:ϕ(x,y)=α((x+y)³+(x−y)³)  (Equation 1)

In Equation 1, α is a scaling coefficient and x and y represent changesin the positing of laser beam 120 in relation to optical fiber 124A inthe corresponding x and y directions where the x-y plane is normal tothe propagation direction of laser beam 120 and the x and y directionsare orthogonal to each other.

In some embodiments, the cubic phase function ϕ can be applied to laserbeam 120 by passing through a diffractive optical element. In someembodiments, the cubic phase function ϕ can be applied to laser beam 120by reflecting off a spatial light modulator or cubic phase mask.Referring now to FIGS. 14A and 14B, an example cubic phase mask and thepropagation of the resulting Airy beam after passing through a focusinglens 108 are shown, respectively. The length and spot size of Airy beam130 can be controlled by the numerical aperture of focusing lens 204 andthe scaling coefficient α. Changes to the focal spot of airy beam 130can be made by adjusting the amplitude of laser beam 120 input after thecubic phase mask. In some embodiments, simultaneous control over thephase and amplitude of laser beam 120 by a single phase mask using acarrier function and altering the phase wrapping of laser beam 120 tochange the first order diffraction efficient of the single phase mask ateach location. In this embodiment, unused laser energy of laser beam 120is directed into other diffractive orders besides the first order and isblocked in the Fourier plane of lens 108 following the single phasemask.

Referring to FIG. 15 , an example laser apparatus 200 is shown. Laserapparatus 200 includes a spatial light modulator 201 followed by anoptical relay 202 (comprising a first lens 204 and a second lens 205)and focusing objective lens 203. As shown, an input beam 120 from laser102 is sent into spatial light modulator 201 where amplitude modulationis introduced via a carrier prism function to direct the desired laserenergy into the first diffractive order off spatial light modulator 201.In some embodiments, other orders are blocked in the Fourier plane ofthe first lens 204 of optical relay 202 via a spatial filter. In someembodiments, laser beam 120 can be rotated by 90 degrees by rotating thecubic phase mask applied to laser beam 120 in spatial light modulator201 to adjust the orientation of laser beam 120 and thereby, adjust Airybeam 130 as applied onto optical fiber 124A or optical fiber array 124.In laser apparatus 200, laser 102 has similar pulse width, output power,pulse energy, and wavelength ranges as discussed above.

Optical relay 202 comprises a first lens 204 and a second lens 205. Likelenses 108, lenses 204, 205 are configured to configured to create anAiry beam 130 and focus Airy beam 130 onto an optical fiber array 124 oroptical fiber 124A and ferrule 131 (also referred to collectively as“optical fiber apparatus 150”) as shown. In alternate embodiments, otherseries and combinations of lenses and/or different lenses (e.g., a pairof collimating lenses) and/or other optics (e.g., spatial lightmodulator (SLM)) may be used to create and focus Airy beam 130 ontooptical fiber array 124 or optical fiber 124A and ferrule 131 (oroptical fiber apparatus 150) and are contemplated in the presentdisclosure.

Focusing lens 203, similar to lenses 204, 205 of optical relay 202, areconfigured to configured to create an Airy beam 130 and focus Airy beam130 onto an optical fiber array 124 or optical fiber 124A and ferrule131 (or optical fiber array apparatus 150) as shown. In particular,focusing lens 203 is configured to control the length and spot size ofAiry beam 130. The length and spot size of Airy beam 130 can becontrolled, in part, by the numerical aperture of focusing lens 108. Insome embodiments, focusing lens has a numerical aperture ranging between0 and 5, between 0 and 3, or between 0 and 1. In alternate embodiments,other series and combinations of lenses and/or different lenses (e.g., apair of collimating lenses) and/or other optics (e.g., spatial lightmodulator (SLM)) may be used to create and focus Airy beam 130 ontooptical fiber array 124 or optical fiber 124A and ferrule 131 and arecontemplated in the present disclosure.

As shown, Airy beam 130 is generated after passing through spatial lightmodulator 201, optical relay 202, and focusing objective lens 203. Airybeam 130 is then applied onto optical fiber 124 in a cutting directionA. As shown, cutting direction A is in the positive z direction,however, it is within the scope of the present disclosure that alternatedirection may be used.

Referring now to FIGS. 16A-16F, Airy beam 130 amplitude shapes (FIGS.16A-16C) and corresponding focal spot shapes (FIGS. 16D-16F) are shown.In particular, FIGS. 16A and 16D show Airy beam 130 without any blockingstructures (e.g., a ferrule) in the path. As shown, the beam amplitudeand shape of Airy beam 130 are unaffected. Referring now to FIGS. 16Band 16E, Airy beam 130 is blocked in the positive y-direction by ablocking structure 131 (e.g., a ferrule 131). As shown, the beamamplitude and shape of Airy beam 130 are unaffected by the presence andorientation of blocking structure 131. Referring now to FIGS. 16C and16F, Airy beam 130 is blocked in the positive x direction by blockingstructure 131 (e.g., ferrule 131). As shown in FIG. 16F, the beamamplitude and shape of Airy beam 130 are aberrated; however, suchaberrations are minimal and less impactful when cleaving optical fiber124 or optical fiber array 124A.

Airy beams 130 provide a method for cleaving (both angled cleave andflat/straight cleave) close to a ferrule end face 132 of ferrule 131. Insome embodiments, perforation 126 (FIG. 3 ) formed by an Airy beam 130is spaced from a ferrule end face 132 by a distance ranging between 1micron and 50 microns, between 1 micron and 25 microns, between 1 micronand 20 microns, or between 1 micron and 10 microns. One advantage ofusing Airy beams 130 is that Airy beam 130 has reduced focal spotaberrations when portions of Airy beam 130 are blocked, such as byferrule 131 for example. In this way, Airy beams can cut close toobjects (i.e., ferrule 131 and ferrule end face 132) withoutexperiencing aberrated focal spot shapes which can cause imperfectionsin the cleave of optical fiber 124A or optical fiber array 124. Also,similar to Bessel beams, Airy beams, when applied onto optical fiber124A or optical fiber array 124, experience refraction as the beams passonto the curved surface of optical fiber 124A or optical fiber array124, and the effects of refraction prevent damaging of optical fiber124A or optical fiber array 124 near the bottom face based on theintensity of the beam.

After creating perforation 126 (FIG. 3 ) on optical fiber assembly 150,optical fiber 124A or optical fiber array 124 may be separated by themethods discussed above in relation to FIGS. 4-5 to create cleavedoptical fiber apparatuses with cleaved optical fibers 124, 124A.Moreover, cleaved optical fibers 124, 124A in this embodiment with Airybeams 130 have substantially the end face surface properties asdescribed above with respect to cleaving with Bessel beams.

Example 1 Relating to Optical Fiber Array 124 Having a 0° C. Leave Angle(Flat Optical Fiber End-Face 127

FIGS. 3 and 6A-9B illustrate representative simulations and images foroptical fiber arrays comprising single mode optical fibers that havebeen cleaved with a flat optical fiber end face (i.e., 0° cleave angle).In particular, the optical fiber array underwent laser-cleaving withmechanical separation by a pressurized air jet as disclosed herein.While this Example relates to an optical fiber array containing singlemode optical fibers, it is within the scope of the present disclosurethat alternate types of optical fiber arrays may be used (e.g., opticalfiber arrays containing multimode optical fibers) to yield theproperties discussed herein.

Referring now to FIGS. 7A-7C, results of a plane-wave decompositionmodel simulation of Bessel beams entering an optical fiber of an opticalfiber array at a perpendicular angle relative to a longitudinal axis ofthe optical fiber with a varying offset in the y-direction (as shown anddefined in FIGS. 7A-7C) are shown. In FIG. 7A, the intensity profiles ofthe beams were combined additively, and a similar optical fiber end facepattern is shown on FIG. 7A as that of rough area RA of optical fiberend face 127 of FIGS. 6A and 6B as discussed below.

Additionally, Bessel beams aligned near the center of the optical fiber(at the optical fiber surface) travelled a shorter distance into theoptical fiber before the paths of the beams are distorted due to thelens effect of the optical fiber discussed previously. Bessel beamsaligned near the edge of the optical fiber experienced refraction sothat their angle bent towards the center of the optical fiber. As shown,these laser beam movement patterns upon contacting the optical fiber andmoving within the optical fiber yield the rough area RA pattern onoptical fiber end face 127 as shown in FIGS. 6A and 6B.

Referring now to FIGS. 7B and 7C, the focal points of the Bessel beamafter propagating halfway through the optical fiber are shown. In FIG.7B, Bessel beam B was launched in the middle of the optical fiber, whilein FIG. 7C, Bessel beam C was launched near the edge of the opticalfiber (an offset in the y-direction equal to one quarter of the diameterof the optical fiber). In both cases, the Bessel beams are turned on ata distance of about 1 centimeter (cm) away from the optical fiber(s). Inthis way, the stage upon which the optical fiber(s) is/are resting canreach a steady velocity before laser treatment of the optical fiber(s).It is contemplated and within the scope of the present disclosure thatthe laser can move at a steady velocity while the stage and opticalfiber(s) are stationary with the stage and the laser being separated bya distance as discussed above. As can be seen, there are distortions inthe focal points of the beam which protects the fiber core from laserdamage. Stated another way, the Bessel beam creates a line of focus onthe optical fiber(s). Bessel beams that contact the optical fiber(s)near/in line with the center of the optical fiber(s) travel a shorterdistance into the optical fiber(s) before distorting as compared toBessel beams near the edge of the optical fiber(s) which are refractedsuch that the Bessel beams' angle bends towards the center of theoptical fiber.

Referring now to FIGS. 8A and 8B, top and side views, respectively, ofmicroscopic images of optical fibers of a laser-cleaved optical fiberarray is shown. Upon examination and measurement of the cleave lengths(based on methods known in the art—e.g., with confocal microscopes), alow variability in cleave length was observed (less than 5 μm)indicating repeatability of the cleaving and separation methodsdisclosed herein. Moreover, symmetrical patterns can be found on theoptical fiber end faces, and the optical fiber end faces aresubstantially identical with one another in the optical fiber array.

Finally, the laser-cleaved optical fiber array samples were inspectedusing a commercial fusion splicer. FIG. 9A shows the images of cleavingquality prior to fusion splicing the optical fiber array sample, andFIG. 9B shows the images of cleaving quality after fusion splicing theoptical fiber array sample. Referring first to FIG. 9A, the opticalfiber array sample on the right was laser-cleaved while the opticalfiber array sample on the left was mechanically cleaved using acommercial mechanical cleaver. The flatness of the laser-cleaved sampleis almost identical to the mechanically cleaved sample as shown by nosignificant angle variation in the X or Y directions for thelaser-cleaved sample. Referring now to FIG. 9B, the spliced opticalfiber array samples show an average estimated insertion loss of about0.01 dB based on optical fiber positioning with each other (i.e.,relative offset between the optical fibers) and/or cleave angle of theoptical fibers indicating that the cleave and separation method asdiscussed herein maintain the quality of the optical fiber end face suchthat fusion splicing of such cleaved optical fibers is possible withlimited insertion loss.

Example 2 Relating to Optical Fiber Array 124 Having a 8° C. Leave Angle(Angled Optical Fiber End-Face 127)

FIGS. 10A-12 illustrate microscopic images for optical fiber arrayscomprising single mode optical fibers that have been cleaved at an angleof about 8° by tilting the upper stage of the stage of the laserapparatus as discussed above. In particular, the optical fiber arrayunderwent laser-cleaving with mechanical separation by a pressurized airjet as disclosed herein. While this Example relates to an optical fiberarray containing single mode optical fibers, it is within the scope ofthe present disclosure that alternate types of optical fiber arrays maybe used (e.g., optical fiber arrays containing multimode optical fibers)to yield the properties discussed herein.

Referring first to FIGS. 10A and 10B, a sample optical fiber array (froma ribbon cable containing 12 optical fibers) was examined under amicroscope after laser-cleaving as described above and prior tomechanical separation. As shown in FIG. 10A, the length of theperforations among each of the optical fibers of the optical fiber arraysample was substantially consistent with limited variability inperforation length. FIG. 10B shows the side view of one of the opticalfibers of the optical fiber array sample of FIG. 10A and illustrates theestimated cleave angle γ of about 8° (8.6°) relative to axis A2 that isperpendicular to the optical fiber axis OA as shown in FIG. 10B.

As mentioned previously, the optical fiber array sample was thenmechanically separated by a pressurized air jet as discussed above. Theoptical fiber array sample was then checked under a microscope with thecorresponding image shown in FIG. 11 . The angle of the fiber core ofthe cleaved array can be estimated using tan⁻¹(Δz/Δx) as indicated,which is about 8.6°. The end angles of the other optical fibers of theoptical fiber array sample were measured and were similar to the meanand angle variation of 8.3°±0.5°. Also, as shown, there is a reducedglass protrusion extending beyond the fiber core on the optical fiberend face. Without wishing to be held to any particular theory, it isbelieved that when the optical fiber(s) are air separated afterlaser-cleaving, the opposite edge relative to the direction of cleaving(also known as “roll-off”) of the optical fiber(s) has a slight inwardcurve relative to the optical fiber end face, which is beneficial inthat such a curve assists greater contact between the core region of theoptical fiber(s) and another optical fiber end face. Stated another way,because the cleaved end is inwardly curved, the maximum glass protrusionbeyond the fiber core is small/minimal, which improves coupling theoptical fiber end face to another optical fiber end face or a waveguide.

Referring now to FIG. 12 , the optical fiber shown was laser-cleaved andthen mechanically separated by tension as discussed above. As shown inthe microscopic image, the cleaved optical fiber end face is almost flatafter tension separation, which indicates that the glass protrusionbeyond the fiber core is large. Such a configuration may be useful forother potential application, such as coupling with special lenses, laserdiode manufacturing, etc.

Example 3 Relating to Water Assisted Laser Angle Cleaving of OpticalFiber Array

Water assisted laser-cleaving is also suitable for making an angledcleave of an optical fiber array. Without wishing to be held to anyparticular theory, it is believed that by immersing the optical fiberarray in liquid during laser perforation processing both sources ofaberration due to index matching between the fiber and water arereduced. FIG. 13A shows a simulation of the intensity profile (seen inXZ plane) of a Bessel beam directed to the center of a tilted opticalfiber end face when assuming the optical fiber is placed in air. FIG.13C shows the intensity profile (seen in XZ plane) of a Bessel beamlaunched to the center of the tilted optical fiber end face while theoptical fiber is immersed in water. When comparing FIGS. 13A and 13C,there are reduced aberrations/distortions of the laser path/direction asthe laser beam passes through the optical fiber in water as compared toair.

Additionally, aberrations/distortions caused by the curved edge of theoptical fiber (shown previously in FIG. 7A) are reduced when the fiberis submerged. Referring briefly to FIG. 13F, twenty (20) Bessel beamswere launched into the fiber at different Y-offsets with respect to thefiber core. As shown, higher energies were experienced in the fiber coreof the optical fiber due to reduced aberrations. This allows the laserbeam to penetrate deeper into the optical fiber, resulting in a greaterportion of the optical fiber being damaged by the laser beam.

Referring now to FIGS. 13B and 13D, an optical fiber end face of theoptical fiber cleaved in the air and an optical fiber end face of theoptical fiber cleaved in water are shown respectively. The opticalfibers were separated using controlled, pressurized air jet separationas discussed herein. These images show that a larger portion of theoptical fiber end face was laser damaged when it was submerged duringcleaving and separation. As shown in the optical fiber that was immersedin water, the rough surface of the optical fiber end face extended tomore than 80% of the optical fiber end face surface area, coveringsubstantially the entire optical fiber core. The roughened fiber coremay further reduce the back reflections when using an 8° final cleaveangled tip for coupling applications (i.e., lensed connectors). If arough core is not desired, the laser may be switched off as it passesover the center of the fiber to prevent core damage.

Referring now to FIG. 13E, a side view image of a water assistedlaser-cleaved optical fiber of an optical fiber array. As shown, areduction in glass protrusion or “roll-off” (circled in FIG. 13E)relative to the optical fiber end face was not observed after waterassisted laser perforation followed by controlled, pressurized air jetseparation.

Example 4 Relating to Laser Cleaving with Airy Beams

Laser apparatus 200 as described above with respect to FIG. 15 was usedto cleave optical fiber 124 or optical fiber arrays 124A of opticalfiber apparatus 150 at a distance of 5 μm from a ferrule end face 131using an Airy beam 130. Simultaneous amplitude and phase shaping using aspatial light modulator (SLM) followed by an optical relay and focusingobjective (with a numerical aperture of 0.6 NA) was used to create anelliptical Airy beam from a Gaussian input beam. Amplitude modulationwas introduced via a carrier prism function. This directed the desiredlaser energy into the first diffractive order exiting the spatial lightmodulator 201 (and the zeroth order exiting the spatial light modulator201 as shown in dashed lines). Other orders are blocked in the Fourierplane of the first lens in the optical relay via a spatial filter. Thelaser 102 had a pulse width of 10 ps, an average power of 40 W, a pulseenergy of 10-200 uJ, a wavelength of 1064 nm, and a Gaussian beam shapediameter of 4 mm. The repetition rate of the laser was reduced via apulse picker such that the pitch between adjacent laser pulses was 3 μm.

Referring to FIGS. 17A-17F, Airy beam 130 shown is not radiallysymmetric. As a result, the aberrations imparted to Airy beam 130 bothwhen entering optical fiber 124 and when being blocked by a ferrule 131depending on the orientation of Airy beam 130. FIGS. 17A-17F showexperimental and simulated results for Airy beams 130 scanned across anoptical fiber with the curve of the beam perpendicular (FIGS. 17A-17C)or parallel (FIGS. 17D-17F) to the cutting direction. The respectivecurves of the beams are adjusted by rotating the cubic phase maskapplied to the beam in the spatial light modulator 201. In both cases,the presence of a ferrule is simulated by blocking the input beam.Referring back briefly to FIGS. 16B and 16C, the beam from FIG. 16B isused for the perpendicular cutting direction (FIGS. 17A-17C) of theoptical fiber, and the beam from FIG. 16C is used for the parallelcutting direction (FIGS. 17D-17F) of the optical fiber.

It can be observed that the beam in FIG. 17C with the curveperpendicular to the cutting direction penetrates deep into the fiber,and its maximum intensity increases with depth due to additionalfocusing elements added by refraction. This leads to excess damage inthe fiber near the exit-point of the laser as seen in FIG. 17B(circled). Conversely, the beam in FIG. 17F with the curve parallel tothe cutting direction aberrates as it penetrates into the fiber similarto a Bessel beam. This protects the fiber from excess damage as shown inFIG. 7E. In addition to protecting the fiber from excess damage, cuttingwith the curve of the beam parallel to the cutting direction ensures aflat cut since the beam does not curve towards the fiber end face.

As also shown in FIGS. 17A-17F, a fiber was damaged by an Airy beam andcleaved at a close to ferrule 131 and ferrule end face 132. A distanceof 20 microns was recorded between the cleaved fiber and the ferrule131. Based on this result, it is contemplated that laser cleaving within5 microns of ferrule 131 and ferrule end face 132 is within the scope ofthe present disclosure.

Referring now to FIGS. 18A and 18B, images of the laser damage that was20 microns from ferrule 131 using an Airy beam and the laser damage lineproximity to ferrule 131 (around 5 microns) are shown, respectively.

There are many other alternatives and variations that will beappreciated by persons skilled in optical connectivity without departingfrom the spirit or scope of this disclosure. For at least this reason,the invention should be construed to include everything within the scopeof the appended claims and their equivalents.

What is claimed is:
 1. A laser-cleaved optical fiber apparatus comprising: at least one optical fiber housed within a ferrule, wherein the ferrule has a ferrule end face, wherein the at least one optical fiber has a fiber end face including an end face core, each fiber end face of the optical fibers having a surface area, the surface area comprising a rough area that defines at least a portion of the surface area, wherein the rough area does not include the end-face core; wherein the rough area has a surface roughness between 0.1 μm and 0.5 μm root mean squared (rms) as measured by a confocal microscope; and wherein the end face of the at least one optical fiber is spaced from the ferrule end face at a distance between 1 micron and 50 microns.
 2. The laser-cleaved optical fiber array of claim 1, wherein for the fiber end face, a remainder of the surface area that excludes the rough area of the fiber end face has a surface roughness of less than 10 nm rms.
 3. The laser-cleaved optical fiber array of claim 1, wherein the rough area of the fiber end face comprises at least 5% of the surface area.
 4. The laser-cleaved optical fiber array of claim 1, wherein the rough area of the fiber end face comprises over 80% of the surface area.
 5. The laser-cleaved optical fiber array of claim 1, wherein the fiber end face has a surface roughness of less than 10 nm rms in the end face core.
 6. The laser-cleaved optical fiber array of claim 1, wherein the fiber end face has a surface roughness of between 0.1 μm and 0.5 μm rms in the end face core.
 7. The laser-cleaved optical fiber array of claim 1, wherein for the at least one optical fiber, the fiber end face has a diameter that is substantially consistent with a diameter of the optical fiber measured at a distance of about 1 mm from the fiber end face, and wherein the fiber end face diameter and the optical fiber diameter have a difference of less than 0.2 μm.
 8. The laser-cleaved optical fiber array of claim 1, wherein the end face core is substantially concentric with a fiber core of the optical fiber measured at a distance of about 1 mm from the fiber end face, and wherein the end face core and the fiber core have an offset at the fiber end face less than 0.1 μm.
 9. The laser-cleaved optical fiber array of claim 1, wherein the fiber end face is substantially flat with a cleave angle between 0 degrees and 15 degrees relative to a longitudinal axis of each optical fiber.
 10. The laser-cleaved optical fiber array of claim 9, wherein the cleave angle has a cleave angle variation of ±0.5 degrees. 